Amino acids are known to be important for the nourishment of the human hair root and the growth of human hair. For example, keratin hydrolysates, a source of amino acids in both free and peptide form, are a common ingredient of hair shampoos and the like. Numerous publications describe the use of an array of amino acids in lotions or tonics for topical application to cure baldness and other skin, scalp and hair disorders.
However, to achieve efficacy from rinse-off hair treatment formulations it is necessary to deliver active ingredients to the site of action, and the benefits attainable are frequently limited for substances such as amino acids, since a large proportion tends to be removed during the rinse stage.
Conventional approaches to this problem have entailed increasing application time, and increasing concentration of the active ingredient in the formulation. For example, Franz et al, Fundam.Appl.Toxicol. 21 (1993) 213-221 demonstrates different rank orders for penetration from various generic prototype personal products formulations as a function of the applied dose. This is not feasible under normal in-use conditions, and can result in barrier damage through prolonged contact time.
There is therefore a need for a rinse-off hair treatment proving enhanced delivery of amino acid.
Metal-amino acid complexes are known and available as such from the prior art. There is a body of literature describing the complexes as a way to administer metals as dietary supplements in a non-toxic way to animals. The amino acid is there to reduce the toxicology profile of heavy metals. In the personal care area, metal-amino acid complexes have been used in hair colouring compositions (Cu or Zn cysteinate, U.S. Pat. No. 4 173,453), antipruritic drugs (zinc-aminoacid conjugates, WO92/10178), and anti-inflammatory creams (SU 1382477). However improved deposition/substantivity of the amino acid portion in a topical formulation is not discussed. GB 937,362 describes compositions for the care and growth of skin, hair and nails containing one or more magnesium compounds of an alpha-aminoacid. The acid residue is described as a carrier for the specific introduction of magnesium into the skin and hair cells. U.S. Pat. No. 4,652,445 describes a no-rinse hair conditioner product with the addition of "zinc-releasing ingredients" to supplement the hair fibre with zinc. The zinc-releasing chemicals may be zinc amino acid complexes, but are preferably zinc-protein or zinc-keratin.
It has now been found that enhanced deposition of amino acid from a rinse-off hair treatment composition can be achieved by incorporation of the amino acid into the composition as a complex with a metal ion. This offers a performance and cost advantage through improved delivery of the amino acid nutrient to the target substrate, ie hair and/or scalp, per unit dose.